Thermobalances have been developed to study, among many purposes, the reaction of gases with other substances. They are used in conjunction with questions of product stability and characterization. Such devices previously developed include a DUPONT THERMALGRAVIMETRIC ANALYZER (TGA) model 951. It has become highly desirable to improve the prior art so as to permit utilization in environments containing corrosive gas. It is to the satisfying of this need that Applicant's invention is directed.